def forward()

in cm/unet.py [0:0]

• 19 lines of code
• 2 McCabe index (conditional complexity)

    def forward(self, qkv, encoder_kv=None):
        """
        Apply QKV attention.

        :param qkv: an [N x (3 * H * C) x T] tensor of Qs, Ks, and Vs.
        :return: an [N x (H * C) x T] tensor after attention.
        """
        bs, width, length = qkv.shape
        assert width % (3 * self.n_heads) == 0
        ch = width // (3 * self.n_heads)
        q, k, v = qkv.chunk(3, dim=1)
        if encoder_kv is not None:
            assert encoder_kv.shape[1] == 2 * ch * self.n_heads
            ek, ev = encoder_kv.chunk(2, dim=1)
            k = th.cat([ek, k], dim=-1)
            v = th.cat([ev, v], dim=-1)
        scale = 1 / math.sqrt(math.sqrt(ch))
        weight = th.einsum(
            "bct,bcs->bts",
            (q * scale).view(bs * self.n_heads, ch, length),
            (k * scale).view(bs * self.n_heads, ch, -1),
        )  # More stable with f16 than dividing afterwards
        weight = th.softmax(weight.float(), dim=-1).type(weight.dtype)
        a = th.einsum("bts,bcs->bct", weight, v.reshape(bs * self.n_heads, ch, -1))
        return a.reshape(bs, -1, length)